As in how to do both! Thomas and I both seem to have a similar problem, oil leaking from the back of the engine, mine is an 8V71 MCI. With Cliffords advice from the other thread in mind I pulled the inspection hatch and from what I see the big connecting hose from the blower to the rear engine cover is there, looks newish (blower is Reliabilt from 2004, replaced at the Detroit dealer in Toronto) with new spring loaded bands to clamp the ends. The little 1/4" pipe mentioned is there with no signs of weeping at all. There is a cross-over tube underneath the large blower hose that looks to be a vent from the heads back down into the valley, not sure what that is about. There is pooling of oil at the base of the blower. The RH valve cover seems very wet (drivers side if I got RH wrong) while the LH is completely dry (I did have it off and cleaned it up 500 miles ago when I was checking injector timing and valve lash and such). I wonder if the valve cover gasket is leaking, I will check that. This after noon I am going to fire it up and observe from the hatch while it's running to see what I see.

So the question is - after you check those blower hose and pipe connections, what are the next most common points of leakage? Particularly that would cause pooling of oil at the base of the blower?

crank case pressure can push oil past seals..take off and clean the ones on both valve covers (vents that is ) easy to pinch gasket on valve covers when reinstalling valve cover gasket.(I've done it) also easy to overtighten ,this leads to smash valve cover gaskets..any hose carrying oil under pressure or not is suspect(or tube)..have found lines to air comp & alt with small leaks..just some I have experienced...Bob

I know when I bought my bus (MC-9), the top of the 8V71 and the drivers side was wet with oil and was leaking pretty bad. It looked like it leaked out a quart of oil while the engine was idling at the fuel island. The passengers side was dry as could be. The PO had 2 of his mechanic climb up in there with a flashlight while I was there. The first mechanic said he could not tell where the oil was coming from but the second mechanic took a shot and guessed it was coming from where the big DN50 Alternator was mounted on to the engine. They pulled the DN50 and replaced the gasket between the alternator and the block and no more leak. It took them a couple hours but it was well worth the wait.

The more i read about this particular oil leak, and the more people i talk to about it, i begin to suspect the head to block o-rings. What have been other peoples experiences with this type of leak? Are the head o-rings a common problem? or am i barking up the wrong tree?

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Only if they were not installed right and 99% of the time they leak at the bottom not the top

well that makes me feel better. there is definitely large amounts of oil leaking at the top somewhere, so I will check on the things previously mentioned and see what can be found. Be doing this right now and report back what i find.

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Reading posts about similar trials on other boards, one person had a leak at the accessory drive location for the alternator, his was a gear driven alternator, and another person had loose blower mounting bolts letting the base gasket leak.

Reading posts about similar trials on other boards, one person had a leak at the accessory drive location for the alternator, his was a gear driven alternator, and another person had loose blower mounting bolts letting the base gasket leak.

Brian

Mine was where the gear driven DN50 alternator adapter plate was bolted onto the engine. It was leaking very bad and running down the drivers side of the engine. Once they pulled the alternator and replaced the gasket, the leak stopped.

I believe the MCI 8 alternators are belt driven not gear driven , when checking for leaks on a 2 stroke clean the engine good first and always run the engine at about 1000 RPMs most of the time it will not show up at idle not enough oil pressure or flow

Bob my 8 was belt driven had 4 -3/8 in wide belts and was air cooled not oil cooled located on the drivers side.50 D gear driven have to be driven off the camshaft where are talking at the top is the blower drive they do have a auxiliary pulley you can belt drive from there but never saw a 50D gear driven mounted there. Fwiw DD uses a special cam for the gear driven 50D and they brake lol just sent Don Fairchild one to replace a broken drive cam for a MCI. A gear driven alternator if it was mine on a 2 stroke would be the 1st to go

well here's what i found...the 1/4" oil tube at the back of the blower was very evident it was leaking. there is an adapter on the back of the blower (3/8" x 1/4" ??). when i put a wrench on the 1/4" tube the adapter spun pretty easy. backed off the nut a little then tightened the adapter and tightened the nut back up. the hydraulic pump bolts were not as tight as they could be, there was evidence of leakage there, so all those bolts got tightened up. the plate on the back and front of the blower got tightened up, those bolts were loose. there is a cover plate on the back of the top of the motor with evidence of leakage and loose bolts, so that got tightened up. the starter bolts were about to fall out, all three bolts went about 3 turns or more just by hand. that one next to the block was a little bugger but i had an old distributor wrench that worked perfectly. at the front of the blower are two little hoses about 1 1/4" or so in diameter. one side had hose clamps, the other had little plastic clips on it that were broken, so i took those off and used bug heavy zip ties for now. (I am parked in the forest far away from any auto parts store, so this will get me to where i can get some hose clamps.) the bolts on the front plate and governor got tightened. there is some kind of motor looking thing under the governor plate that was loose. the left side (standing at the back of the bus) valve cover is leaking, and the oil sending unit is leaking really bad.

there are two oil sending units on the oil manifold attached to the frame rail. one is very large, the other one small. both have one wire attached. the one that is leaking is the smaller one. can i get this at a napa or other box store? anyone have a part number that will cross to a box store part or is this a DD order item?

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Derick, you probably still have a leak on the supply tube it has rubber compression seals on each end and that tube slides to remove the blower no flares just a straight pipe you do need to replace those seals if you get close to a DD dealer they are about a buck for both.